This invention relates generally to the field of organometallic compounds. In particular, this invention relates to the preparation of organometallic compounds suitable for use in vapor deposition and epitaxial growth of metal-containing films.
Metal films may be deposited on surfaces by a variety of means such as chemical vapor deposition (“CVD”), physical vapor deposition (“PVD”), and other epitaxial techniques such as liquid phase epitaxy (“LPE”), molecular beam epitaxy (“MBE”), chemical beam epitaxy (“CBE”) and atomic layer deposition (“ALD”). Chemical vapor deposition processes, such as metalorganic chemical vapor deposition (“MOCVD”), deposit a metal layer by decomposing organometallic compounds (often referred to as “precursors”) at elevated temperatures, i.e., above room temperature, either at atmospheric pressure or at reduced pressures. A wide variety of metals may be deposited using such CVD or MOCVD processes.
For semiconductor and electronic device applications, these organometallic compounds must be highly pure and be substantially free of detectable levels of both metallic impurities, such as silicon and zinc, as well as oxygenated impurities. Oxygenated impurities are typically present from the solvents, such as ethereal solvents, used to prepare such organometallic compounds, and are also present from other adventitious sources of moisture or oxygen.
Organometallic compounds of Group IIB and IIIA metals may be prepared by a variety of conventional methods. Such methods include reacting a Group IIB or IIIA metal halide with a Grignard reagent in an ethereal solvent, reacting an organo halide with a metal melt, and transalkylating a metal halide using a trialkyl aluminum, among other methods. Transalkylation reactions, such as those disclosed in U.S. Pat. Nos. 5,756,786, and 6,770,769 are particularly useful as ethereal solvents can be avoided.
When transmethylation reactions are employed using a Group IIIA metal trihalide, such as indium trihalide, and trimethyl aluminum, the reaction is not efficient with respect to the methyl groups transferred. For one mole of indium trihalide, three moles of trimethyl aluminum must be used. The resulting byproducts are also difficult to separate from the desired reaction product, trimethyl indium. Accordingly, improved methods of manufacturing Group IIB and IIIA compounds are needed.